Semiconductor integrated circuit and semiconductor integrated circuit manufacturing method

ABSTRACT

An RF amplifier circuit  21  for amplifying AM broadcast signals is constituted by use of cascaded P channel MOSFETs  4  and  5 . This cascade connection realizes a reduction of the feedback capacitance between the source and gate of the P channel MOSFET  4 , thereby providing a stable operation. Further, using the P channel MOSFETs to constitute the amplifier circuit realizes a reduction of flicker noise and allows the amplifier circuit to be manufactured by the same CMOS process as the CMOS digital circuit.

TECHNICAL FIELD

The present invention relates to a semiconductor integrated circuithaving an amplifier circuit for amplifying AM broadcast signals and themethod of manufacturing the same.

BACKGROUND ART

The configuration of a conventional AM-broadcast receiving circuit isshown in FIG. 5. FIG. 5(a) shows the configuration of a tuning circuitmethod, and FIG. 5(b) shows the configuration of an aperiodic circuitmethod.

The AM-broadcast receiving circuit of the tuning circuit method shown inFIG. 5(a) comprises a capacitor 101, a resistor 102, an FET (fieldeffect transistor) for signal amplication 103, a tuning circuit 104, andan IC 106. An RF amplifier comprises the capacitor 101, resistor 102,FET for signal amplification 103, and tuning circuit 104 among all thesecomponents.

The capacitor 101 is used to cut the DC component of AM broadcastsignals inputted from an antenna which is not shown in FIG. 5, andcomprises a tuning capacitor C1 and tuning coils L1 and L2. One end ofthe tuning circuit 104 is connected to a power source Vcc. The IC 106inputs an RF amplifier signal outputted from the tuning circuit 104, andimplements the signal processing at a later step necessary to receive AMbroadcast signals including mixing and frequency conversion.

The AM-broadcast receiving circuit of an aperiodic circuit methodcomprises the capacitor 101, resistor 102, FET for signal amplification103, coupling capacitor 105, IC 106 and coil 107, as shown in FIG. 5(b).The RF amplifier comprises the capacitor 101, resistor 102, FET forsignal amplification 103, coupling capacitor 105 and coil 107 among allthese components.

In recent years, integration of an RF circuit has been promoted in aradio terminal which handles a high-frequency signal in 2.4 GHz and 5GHz bands, and an LSI has been developed which integrates an RF circuitwhich used to be externally mounted as an individual analog part intoone chip by means of a MOS technology. Furthermore, an LSI whichintegrates an RF circuit by means of a MOS technology has been developedin an FM broadcast receiver which uses a frequency band from 76 MHz to90 MHz. An RF amplifier is also included in the RF circuit which isintegrated into one chip.

In an AM broadcast receiver which uses a low-frequency signal in a MFband from 530 kHz to 1,710 KHz and in a LF band from 153 KHz to 279 KHz,since the frequency bands exist in the region in which a flicker noisecomponent is large, it was considered difficult to constitute an RFamplifier using MOSFETs.

Consequently, the conventional RF amplifier of an AM broadcast receiverwas designed using a junction type FET (JFET) 103 as the RF amplifier orcombining the JFET and a bipolar transistor, as shown in FIG. 5.

However, since JFET differs from MOS in the manufacturing process, andcannot be integrated into one chip, the JFET was mounted outside of thechip of an IC 106 as an individual part. As a result, there was aproblem in that an RF circuit of a high-frequency radio terminal cannotbe miniaturized.

Furthermore, since an AM amplifier circuit amplifies a feeble signal, itis desired to give a stable bias to an FET against the fluctuations,etc. of a power-supply voltage.

DISCLOSURE OF THE INVENTION

The purpose of the present invention is to integrate an amplifiercircuit for amplifying AM broadcast signals and a CMO digital circuitinto one chip. Another purpose of the present invention is to stabilizethe bias of an AM amplifier circuit.

The semiconductor integrated circuit of the present invention has anamplifier circuit of AM broadcast signals which comprises a first Pchannel MOSFET for amplifying AM broadcast signals and a second Pchannel MOSFET cascade-connected to the first P channel MOSFET, and aCMOS digital circuit.

According to the present invention, using a P channel MOSFET realizes areduction of the flicker noise of the amplifier circuit for amplifyingAM broadcast signals, and allows the amplifier circuit of the AMbroadcast signals and the CMOS digital circuit to be integrated into onechip by, for example, a CMOS process.

Another semiconductor integrated circuit of the present invention has anamplifier circuit of AM broadcast signals comprising a first P channelMOSFET for amplifying AM broadcast signals and a bias circuit for givinga specific bias to the first P channel MOSFET, and a CMOS digitalcircuit, and forms the first P channel MOSFET, the bias circuit, and theCMOS digital circuit on the same circuit board by a CMOS process.

According to this invention, the flicker noise of the amplifier circuitfor amplifying AM broadcast signals can be reduced, and the amplifiercircuit of the AM broadcast signals and the CMOS digital circuit can beintegrated into one chip by the CMOS process. Furthermore, a stable biascan be given to the first P channel MOSFET against the fluctuations,etc. of a power-supply voltage.

In the above-mentioned invention, the semiconductor integrated circuithas an AGC circuit which controls the amplification degree of the secondP channel MOSFET.

Constituting the semiconductor integrated circuit in this way makes itpossible to implement the AGC control of the amplification degree of thesecond P channel MOSFET, for example, according to the level of a signalreceived.

In the above-mentioned invention, the bias circuit has a third MOSFETwhich constitutes the first P channel MOSFET and a current mirrorcircuit.

Constituting the bias circuit in this way makes it possible to set thecurrent which flows through the first P channel MOSFET and the currentwhich flows through the third MOSFET in a specific proportionalrelation. Thus, the bias of the first P channel MOSFET can be stabilizedagainst the fluctuations, etc. of a power-supply voltage.

In the above-mentioned invention, the bias circuit has the third MOSFETwhich together with the first P channel MOSFET constitutes the currentmirror circuit, and makes the ratio of the channel width of the thirdMOSFET to the channel width of the first P channel MOSFET 1:k (k≧1).

Constituting the bias circuit in this way, for example, when the channellength is made the same, can make a current as much as k times of thecurrent flowing through the third MOSFET flow through the first Pchannel MOSFET, and can stabilize the bias of the first P channelMOSFET.

In the above-mentioned invention, the bias circuit is constituted insuch a way that the source is connected to a power-supply voltage, thedrain is connected to a constant-current power supply, and the gate isconnected to the constant-current power supply.

Constituting the bias circuit in this way can keep the current flowingthrough the third MOSFET constant, so the current flowing through thefirst P channel MOSFET can be kept constant. Thus, the operating pointof the first P channel MOSFET can be stabilized against thefluctuations, etc. of a power-supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of an RF amplifier circuit in a firstembodiment.

FIG. 2 is a block diagram showing an AM-receiver IC in a firstembodiment.

FIG. 3 is an explanatory drawing of flicker noise.

FIG. 4 shows the configuration of an RF amplifier circuit in a secondembodiment.

FIG. 5 shows the configuration of a conventional AM-broadcast receivingcircuit.

BEST MODE FOR CARRYING OUT THE INVENTION

Described below are the embodiments of the present invention withreference to the drawings.

FIG. 1 shows the configuration of an RF amplifier circuit 21 whichamplifies AM broadcast signals in a first embodiment.

AM broadcast signals which are received by an antenna which is not shownin FIG. 1 are inputted to one end of a capacitor 1, as shown in FIG. 1.The other end of the capacitor 1 is connected to the gate of the Pchannel MOSFET (first P channel MOSFET) 4. The capacitor 1 is used tocut the DC component of AM broadcast signals.

The voltage in which a power-supply voltage is divided by a resistor 2and a resistor 7 is supplied to the gate of a P channel MOSFET 4 as abias voltage. The resistor 2 and the resistor 7 are connected in series,the other end of the resistor 2 is connected to the power supply Vcc,and the other end of the resistor 7 is grounded.

A P channel MOSFET (second P channel MOSFET) 5 is cascade-connected tothe P channel MOSFET 4. A resistor 3 connected to the power supply Vccand the drain of a N channel MOSFET 9 which will be explained later areconnected to the gate of the P channel MOSFET 5. Also, a bypasscapacitor 10 is connected to the gate of the P channel MOSFET 5, and theother end of the capacitor 10 is grounded.

The cascade-connection of the P channel MOSFET 4 and the P channelMOSFET 5 realizes a reduction of the feedback capacitance between thegate and source of the P channel MOSFET 4, thereby improving thehigh-frequency characteristics of the P channel MOSFET 4.

A tuning circuit 6 is connected to the drain of the P channel MOSFET 5.The tuning circuit 6 comprises a tuning capacitor C1 and tuning coils L1and L2, and selects and outputs the frequency of AM broadcast signalswhich are controlled by the AGC circuit and are outputted from the Pchannel MOSFET 5. The other ends of the tuning capacitor C1 and thetuning coils L1 and L2 are grounded.

The P channel MOSFET 4 and the P channel MOSFET 5 constitute the RFamplifier circuit 21 for amplifying the AM broadcast signals.

An AGC current I AGC which controls the gain of the RF amplifier circuit21 is inputted to the drain of the N channel MOSFET 8 from the AGC (autogain control) circuit which is not shown in FIG. 1. The drain and gateof the N channel MOSFET 8 are connected, and the source is grounded.

The gate of a N channel MOSFET 9 is connected to the gate of the Nchannel MOSFET 8. The drain of the N channel MOSFET 9 is connected tothe gate of the P channel MOSFET 5, and the source is grounded.

The N channel MOSFET 8 and the N channel MOSFET 9 constitute the currentmirror circuit, and a current proportional to the AGC current I AGCwhich flows into the drain of the N channel MOSFET 8 flows through the Nchannel MOSFET 9.

Thus, the bias voltage of the P channel MOSFET 5 changes according tothe AGC current I AGC which is outputted from the AGC circuit, theamplification degree of the P channel MOSFET 5 is controlled thereby,and the level of the RF signal to be outputted changes thereby.

The gate of the P channel MOSFET 5 does not necessarily need to becontrolled by the AGC, but may be, for example, a fixed bias.

The RF amplifier circuit 21 is integrated into one chip together with acircuit which implements a signal processing at a later step necessaryto receive AM broadcasting including mixing, frequency conversion, etc.a latch circuit which will be described later, and a digital circuitsuch as a shift register, and the output signal of the tuning circuit 6is outputted to a mixer circuit which will be described later, etc.

Next, described below is the operation of the RF amplifier circuit 21which is constituted as described above.

The DC component of the AM broadcast signals inputted from an antennawhich is not shown in FIG. 1 is cut by the capacitor 1, and the ACcomponent is amplified by the P channel MOSFET 4. Then, the RF signaloutputted from the P channel MOSFET 4 is amplified to a specific levelby the P channel MOSFET 5 which is controlled by the AGC circuit and isoutputted to the tuning circuit 6.

In other words, a current I1 corresponding to the source current I AGCof the N channel MOSFET 8 flows to the source of the N channel MOSFET 9.The larger the value of the current I AGC is, the larger the value ofthe corresponding current I1 becomes, and the bias voltage of the Pchannel MOSFET 5 changes. Thus, a voltage VDS between the drain andsource of the P channel MOSFET 4 changes, and the VDS is lowered and thegain is controlled.

According to the amplifier circuit for AM broadcasting in the firstembodiment, the cascade-connection of the P channel MOSFET 4 and the Pchannel MOSFET 5 realizes a reduction of the feedback capacitance Cgdbetween the source and gate of the P channel MOSFET 4. Thus, thehigh-frequency characteristics of the P channel MOSFET 4 can beimproved, and the stability of the amplifier circuit 21 can beincreased.

Furthermore, connecting the output of the AGC circuit to the gate of theP channel MOSFET 5 makes it possible to control the amplification degreeof the P channel MOSFET 5 by an AGC signal, and makes the level of an RFsignal constant.

The tuning circuit 6 amplifies the constant-level RF signal outputtedfrom the second P channel MOSFET 5, and outputs the amplified RF signalto a mixer in the following step which is not shown in FIG. 1. In thesubsequent signal processing circuit (not shown in FIG. 1) including themixer and the frequency conversion unit, the remaining processingnecessary to receive AM broadcasting is implemented, and a station forthe input signal is selected, then the signal is amplified, demodulated,etc. at an output step, and is outputted as an audio signal.

FIG. 2 is a block diagram showing the AM-receiver IC (semiconductorintegrated circuit) 31 in which both the amplifier circuit for AMbroadcasting 21 comprising the P channel MOSFET and the CMOS digitalcircuit are integrated into one chip.

This AM-receiver IC 31 forms an input circuit 23 which selects afrequency for the signal inputted from an antenna 12, the RF amplifiercircuit 21 which amplifies AM broadcast signals, FM and AM receivingcircuits comprising a MIX circuit 24 which converts the AM broadcastsignals amplified by the RF amplifier circuit 21 into a mediumfrequency, a CMOS digital circuit comprising a latch circuit 25, a shiftregister 26, a PLL synthesizer 27, a frequency counter 28, etc. on onechip by means of a CMOS process.

FIG. 3 shows the flicker noise characteristics of the JFET, P channelMOSFET, and N channel MOSFET.

Flicker noise which is the internal noise of a MOS semiconductor becomeslarge in its noise level in inverse proportion to its frequency, asshown in FIG. 3. Consequently, if the RF amplifier is constituted by aMOS circuit when the signal to be handled is a low-frequency signal suchas AM broadcast signals, the noise level is higher compared with whenthe JFET is used.

However, when the N channel MOSFET and the P channel MOSFET arecompared, the P channel MOSFET is small in its noise level even in alow-frequency region than the N channel MOSFET. In the embodiment of thepresent invention, the level of flicker noise is kept at a comparativelylow level by constituting the RF amplifier circuit 21 for amplifying AMbroadcast signals by the P channel MOSFET.

In addition, since the P channel MOSFET can be made in the process ofmanufacturing CMOSs, it is possible to integrate into one chip the CMOScircuit such as a receiving circuit of AM broadcast signals includingthe RF amplifier circuit 21, the latch circuit 25, the shift register26, etc., and it is possible to miniaturize the circuit of the receiver.Also, since the whole of the circuits of radio equipment can be made bythe same CMOS process, the manufacturing process can be simplified andthe manufacturing cost can be reduced.

FIG. 4 shows the configuration of an RF amplifier circuit 31 in a secondembodiment of the present invention. In the explanation of FIG. 4, thesame number or mark is given to the same constituent as in FIG. 1 toomit a detailed explanation of the constituent.

What is different between the circuit shown in FIG. 4 and that shown inFIG. 1 is that the AGC control voltage VAGC outputted from the AGCcircuit which is not shown in FIG. 4 is inputted to the gate of the Pchannel MOSFET 5 and that a bias circuit 42 constituting the currentmirror circuit together with the P channel MOSFET 4 is provided.

In FIG. 4, the AGC control voltage VAGC is inputted to the gate of the Pchannel MOSFET 5 via the resistor 40; the voltage VDS between the drainand source of the P channel MOSFET 4 changes according to this AGCcontrol voltage VAGC; and the gain is controlled by lowering the VDS.For your information, VDS=Vcc−(VAGC+VGS5), and VGS5 is the voltagebetween the gate and source of the P channel MOSFET 5.

The bias circuit 42 comprises the P channel MOSFET 43 including aconstant-current power supply 44.

The source of the P channel MOSFET 43 is directly connected to the powersupply Vcc, the drain is connected to the constant-current power supply44, and the gate is connected to the drain. Also, the gate of the Pchannel MOSFET 4 is connected to the gate of P channel MOSFET 4 via theresistor 45.

The resistor 45 connected in series to the gate of the P channel MOSFET43 is used for AM broadcast signals not to go around the P channelMOSFET 43 and to raise the input impedance of the P channel MOSFET 4.

Since the P channel MOSFET 4 and the P channel MOSFET 43 constitute thecurrent mirror circuit, when the channel area of both P channel MOSFET 4and P channel MOSFET 43 is equal, the current flowing through both Pchannel MOSFET 4 and P channel MOSFET 43 becomes equal.

Then, when the channel length of the P channel MOSFET 4 is L1, thechannel width is W1, the channel length of the P channel MOSFET 43 isL2, and the channel width is W2, the respective channel lengths andchannel widths are set so that the relations of L1=L2, and W1=k·W2 (k≧1;k is a fixed number larger than 1 in the embodiment) are establsished.The fixed number k is set so that the gain of the first P channel MOSFET4 which is cascade-connected becomes optimum.

The RF amplifier circuit 41 in a second embodiment can reduce thefeedback capacitance of the P channel MOSFET 4 and enhance the stabilityof the RF amplifier circuit 41 by cascade-connectig the P channel MOSFET4 and P channel MOSFET 5, both of which amplify the AM broadcastsignals, in the same way as in the first embodiment.

Also, constituting the current mirror circuit by the P channel MOSFET 4and the P channel MOSFET 43 of the bias circuit 42 makes it possible tosupply a stable bias to the P channel MOSFET 4. Thus, the bias of the Pchannel MOSFET 4 can be stablized against the fluctuations, etc. of apower-supply voltage.

Furthermore, setting the channel width of the P channel MOSFET 43 of thebias circuit 42 to 1/k of the channel width of the P channel MOSFET 4,when a current of 1/k is made to flow to the p channel MOSFET 43, canmake a current as much as k times flow to the P channel MOSFET 4. Also,connecting the constant-current power supply 44 to the drain of the Pchannel MOSFET 43 can keep the current flowing to the P channel MOSFET43 constant. Thus, the operating point of the P channel MOSFET 4 can bestabilized against the fluctuations of the power-supply voltage and thechanges of temperature, etc.

The present invention maybe constituted as follows without being limitedto the embodiment described above. (1) The amplifier circuit of AMbroadcast signals related to the present invention may be mounted notonly on an IC for an AM receiver, but also on an IC for communicationswhich is used for a cellular phone and a radio LAN which have a radioline corresponding to a higher frequency. (2) The bias circuit 42 may benot only a current mirror circuit comprising the p channel MOSFET or theN channel MOSFET and the current power-supply 44, but also any circuitif it can stablize the bias.

According to the present invention, it is possible to suppress theflicker noise in the frequency bandwidth of AM broadcasting andintegrate the amplifier circuit of AM broadcast signals and the CMOSdigital circuit into one chip. Furthermore, it is possible to stabilizethe bias against the fluctuations, etc. of a power-supply voltage byproviding a bias circuit.

1. A semiconductor integrated circuit, comprising an amplifier circuitof AM broadcast signals having a first P channel MOSFET for amplifyingAM broadcast signals and a second P channel MOSFET cascade-connected tothe first P channel MOSFET; and a CMOS digital circuit.
 2. Asemiconductor integrated circuit, comprising: an amplifier circuit of AMbroadcast signals having a first P channel MOSFET for amplifying AMbroadcast signals and a second P channel MOSFET cascade-connected to thefirst P channel MOSFET; and a CMOS digital circuit; wherein the first Pchannel MOSFET, the second P channel MOSFET and the CMOS digital circuitare formed on the same circuit board by a CMOS process.
 3. Asemiconductor integrated circuit, comprising: an amplifier circuit of AMbroadcast signals having a first P channel MOSFET for amplifying AMbroadcast signals and a bias circuit for giving a specific bias to thefirst P channel MOSFET; and a CMOS digital circuit; wherein the first Pchannel MOSFET, the bias circuit and the CMOS digital circuit are formedon the same circuit board by the CMOS process.
 4. A semiconductorintegrated circuit, comprising; an amplifier circuit of AM broadcastsignals having a first P channel MOSFET for amplifying AM broadcastsignals, a second P channel MOSFET cascade-connected to the first Pchannel MOSFET and a bias circuit for giving a specific bias to thefirst P channel MOSFET; and a CMOS digital circuit, wherein the first Pchannel MOSFET, the second P channel MOSFET, the bias circuit and theCMOS digital circuit are formed on the same circuit board by the CMOSprocess.
 5. The semiconductor integrated circuit according to claim 1,which has an AGC circuit for controlling the amplification degree of thesecond P channel MOSFET.
 6. The semiconductor integrated circuitaccording to claim 2, wherein the bias circuit has the third MOSFETwhich together with the first P channel MOSFET constitutes a currentmirror circuit.
 7. The semiconductor integrated circuit according toclaim 6, wherein the bias circuit has the third MOSFET which togetherwith the first P channel MOSFET constitutes a current mirror circuit,and makes the ratio of the channel width of the third MOSFET to thechannel width of the first P channel MOSFET 1:k (k≧1).
 8. Thesemiconductor integrated circuit according to claim 6, wherein the biascircuit is constituted in such a way that one end of either the drain orthe source is connected to a power-supply voltage, the other end ofeither the drain or the source is connected to the constant-currentpower supply, and the gate is connected to the constant-current powersupply.
 9. A method of manufacturing a semiconductor integrated circuitwhich forms a first P channel MOSFET for amplifying AM broadcast signalsand a second P channel MOSFET cascade-connected to the first P channelMOSFET, and a CMOS digital circuit on the same circuit board by the CMOSprocess.
 10. The method of manufacturing a semiconductor integratedcircuit, wherein an AGC circuit for controlling the amplification degreeof the second P channel MOSFET is provided.
 11. The method ofmanufacturing a semiconductor integrated circuit according to claim 9,which forms the third MOSFET and the second P channel MOSFETconstituting a current mirror circuit, and which makes the ratio of thechannel width of the third MOSFET to the channel width of the first Pchannel MOSFET 1:k (k≧1).
 12. The semiconductor integrated circuitaccording to claim 2, which has an AGC circuit for controlling theamplification degree of the second P channel MOSFET.
 13. Thesemiconductor integrated circuit according to claim 4, which has an AGCcircuit for controlling the amplification degree of the second P channelMOSFET.
 14. The semiconductor integrated circuit according to claim 3,wherein the bias circuit has the third MOSFET which together with thefirst P channel MOSFET constitutes a current mirror circuit.
 15. Thesemiconductor integrated circuit according to claim 4, wherein the biascircuit has the third MOSFET which together with the first P channelMOSFET constitutes a current mirror circuit.